1. Field of the Invention
This invention relates to a casing drive apparatus, and in particular to a drive apparatus for use with plastic pipe in a water well.
2. Discussion of the Prior Art
In general, in the past well casings for water or oil wells were formed of metal. With the advent of modern plastics, casing for use in water wells are being formed of plastic. When drilling a water well, it is important to effect a good seal between the bottom of the surface casing and the adjacent formation to prevent the ingress of loose surface formation material, water and containments into the well casing. When using plastic casing, the seal is formed by a rubber cup and bentonite, a cement group or other sealants for preventing the entry of surface water into the well casing. In order to form a good seal, a common practice is to pound the casing against the bottom of the well bore. Following drilling, a heavy weight controlled by the drilling rig is transferred to the casing to press the casing against the formation. When plastic pipe is used in a water well, hammering against the casing is likely to cause fracturing of the plastic pipe sections defining the well casing.
If the well being drilled is dry or yields bad water, the casing is removed from the well. When plastic pipe is used to define the casing, it is difficult to remove such pipe from the bore. The pipe sections, which are approximately twenty feet long, commonly stick to the sides of the bore and break under pressure.
3. General Description of the Invention
The object of the present invention is to provide a solution to the above identified problems in the form of a relatively simple casing drive apparatus which can be used to push a plastic drill casing downwardly into a well bore to effect a tight seal or alternatively to remove the casing from the well bore without damaging the casing. At the very least, the casing drive apparatus of the present invention reduces the likelihood of damage to the well casing during downward movement into the well bore or removal of the casing from the bore.
Accordingly, the present invention relates to an apparatus for driving a well casing comprising shoe means for attachment to the bottom end of a well casing; shoulder means in said shoe means; drive sub means for insertion into a drill pipe string slidable in said well casing and in said shoe means; dog means pivotal in said sub means for engaging said shoulder means; and spring means for biasing said dog means outwardly into engagement with said shoulder means, whereby, when said sub means is slid into said shoe means and said dog means engages said shoulder means, vertical force exerted on said sub means will cause said dog means to bear against said shoulder means to effect vertical movement of said shoe means and consequently of the well casing.